The present invention relates to a method for improving a doping profile for gas phase doping and, in particular, to a method for improving a doping profile for gas phase doping used to produce a trench capacitor in a semiconductor memory cell.
Particularly when producing trench capacitors in semiconductor memory cells for integrated circuits, such as memories with random memory access (RAM random access memory), dynamic memories (DRAM, dynamic random access memory), synchronous dynamic memories (SDRAM, synchronous DRAM), etc., the production of a xe2x80x9cburied platexe2x80x9d requires doping profiles which have sufficiently high doping concentrations even at relatively great depth.
Normally, such doping was carried out in a lower region of the trench capacitor using xe2x80x9cAsG depositionxe2x80x9d, structuring of the AsG layer and a subsequent high temperature step in order to diffuse out the arsenic into the substrate. This allowed the doping to be limited to the lower part of the trench capacitor, with relatively great penetration depths into the substrate being achievable. Such AsG deposition is costly, however, and impinges upon technical boundaries particularly for future technology shrinks, for example on account of poor edge coverage.
To produce such a buried plate (outer electrode of the trench capacitor), doping methods using gas phase doping have also been proposed, which allows an integration density to be advanced further in principle. However, a drawback of such a conventional method for carrying out gas phase doping is a low and unstable doping level, which results in a severe limitation to suitability for mass production.
It is accordingly an object of the invention to provide a method for improving a doping profile for gas phase doping which overcomes the above-mentioned disadvantages of the prior art methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for improving a doping profile. The method includes the steps of providing and preparing a semiconductor substrate; introducing in a process chamber silicon nitride and/or products of decomposition from a silicon nitride deposition; and carrying out a gas phase doping in the process chamber.
Particularly the introduction of silicon nitride and/or products of decomposition from a silicon nitride deposition in a process chamber allows a doping level to be stabilized for gas phase doping carried out at the same time or subsequently, which makes the process suitable for mass production. In particular, this results in very high doping levels at a great depth in a semiconductor substrate.
Preferably, a silicon nitride layer is deposited in the process chamber, which allows the doping process to be significantly improved for gas phase doping.
Alternatively, ammonium chloride crystals or small amounts of HCl and/or NH3 can be introduced into the process chamber as products of decomposition from the silicon nitride deposition, which again allows the doping levels for gas phase doping to be significantly stabilized and makes them suitable for mass production.
Preferably, the gas phase doping is carried out in a low-pressure range, which allows the dopant concentration to be increased further and permits further reductions in the size of the technological structure. Specifically, the gas phase doping is carried out in a pressure range of 13.33 pascals to 133.3 kpascals and a temperature range of 800 to 1100xc2x0 C.
To implement arsenic gas phase doping, AsH3 in a carrier gas containing He/Ar can be used, for example. Such process gases are normally present anyway in a large number of standard processes and thus facilitate implementation of the method in standard processes.
Alternatively, the carrier gas used can also be H2, the result of which is an improved surface roughness, particularly in the case of gas phase doping in the low-pressure range. Particularly when implementing further technology shrinks, such improved surface roughnesses for the substrate allow extensive compensation for the associated undesirable reduction in capacitance when producing trench capacitors, for example.
In accordance with an added mode of the invention, there is the step of carrying out the gas phase doping as an arsenic gas phase doping, a phosphorus gas phase doping or a boron gas phase doping.
In accordance with another mode of the invention, there is the step of using 0.1-5% AsH3 in the carrier gas during the gas phase doping.
In accordance with a further mode of the invention, during the gas phase doping, a temperature range is 900xc2x0 C. to 950xc2x0 C., a pressure range is 0.133 to 13.3 kpascals, a gas flow range is 200 to 400 sccm of 0.5-1% of a doping gas in a carrier gas, and a diffusion time range is 30 to 120 minutes.
In accordance with a concomitant mode of the invention, there are the steps of forming a trench in the semiconductor substrate, and forming an insulating collar in an upper region of the trench.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for improving a doping profile for gas phase doping, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.